Induction furnace



June 16, 1942. H. c. FISHER 2,286,481

INDUCTION FURNACE Filed July 5, 1940 HENRY 2F/5 HER Patented June 16,1942 UNITED STATES PATENT OFFICE INDUCTION FURNACE Henry C. Fisher,Worcester, Mass., assignor to Norton Company, Worcester, Mass., acorporation of Massachusetts Application July 5, 1940, Serial No.343,923

1 Claim.

'I'he invention relates to induction furnaces.

One objectof the invention is to provide an induction furnace with anair cooled wall supplementary to the water cooled coil. Another objectofthe invention is to provide an induction furnace lining with coolingducts inside of the coils and incorporated in the lining.

A further object of the invention is to provide a safer inductionfurnace. Another object of the invention is to create a sharper heatgradient between the outside and the inside of induction furnaces.Another object of the invention is to trap any molten metal which mayleak through the lining of an induction furnace before it comes incontact with the induction coil.

Another object of the invention is to cause freezing of the slagconstituents and metal inside of the refractory lining of an inductionfurnace to stop the approach of molten metal to the induction coil.Another object of the invention is to provide a path of escape for anymetal that has penetrated through thev refractory lining, thereby savingthe induction coil from damage and warning'the operator to shut off thepower.

Another object of the invention is to provide an induction furnace witha stronger wall so that the lining can be rammed in place without dangerof breaking the wall or damaging the coil. Other objects will be in partobvious or in part pointed out hereinafter.

The invention accordingly consists in the features of construction,combinations of'elements, and arrangements of parts, all as will beillustratively described herein, and the scope of the applicationofwhich will be indicated in the following claim.

In the accompanying drawing showing one of many possible embodiments ofthe mechanical features of the invention,

Figure l is a vertical axial sectional view of a furnace constructed inaccordance with this invention, and

Figure 2 is a crosssectional view taken on the line 2-2 of Figure 1.

The present invention is more particularly concerned with inductionfurnaces which have only a primary coil, current being induced in themetal charge thereby heating it. It has been customary to run suchfurnaces on frequencies of 480 or 960 cycles, the primary coil being aspiral metal tube through which water is flowing. In the manufacture ofsuch furnaces it has been common to place a sheet mica or asbestoscylinder inside of the coil, then to pour refractory granular material,referred to as cement,

into the inside of the furnace and tamp to form a bottom. Thereafter aCrucible core either of graphite or of metal would be set in place and amore refractory mixture tamped outside of this core and inside of themica or asbestos cylinder. 'I'he electric circuit would then becompleted and eddy currents induced in the Crucible core would sinterthe refractory material next to it.

Such furnaces have frequently failed in the past due to a crack formingin the sintered lining, the molten metal eventually reaching the watercooled primary coil. It is to be understood that after the furnace hasbeen in operation a short time the sheet iron core which was originallyintroduced no longer exists.

Considering now the present invention and referring to Figure 1, Iprovide a furnace bottom I0 which may be made of any suitable refractory material such as insulating bricks. I provide a pair ofasbestos cylinders II and I2 pf slightly different diameters, locatingone inside the other as shown in Figure 1. These may be held apart bysuitable asbestos spacers I3. The cylinder I 2 is longer than thecylinder II and extends above it as shown in Figure 1. These may be heldapart by suitable asbestos spacers I3. The cylinder I2 is longer thanthe cylinder II and extends above it as shown in Figure l, while bothcylinders rest upon the refractory bottom I0. These two cylinders II andI2 together constitute a furnace wall having air passages for thecooling of refractory lining and for the escape of metal which maypenetrate the lining. l

I further provide an asbestos box including sides' I 4 and a bottom I5which may be held together with suitable metal angles I6. This box maybe rectangular in shape while the furnace proper is cylindrical. Insidethe box and around the outer asbestos clyinder I I is a coil 2'0, forexample of copper tubing.' The turns of the coil 20 are separated bysuitable insulating material 2l, for example a strip of asbestos ormica.

One end of the coil 20 is connected to a water supply and the other endis connected to waste in any suitable manner, as is understood in thisart.

I form a number of depressions in the bottom I0 which are connected withoricesl through the outer asbestos sides I4. Extending between thecylinders II and I2 is a. semi-circular annular bustle pipe 21 which mayalso be made of asbestos and may be cemented to the cylinders Il and I2.A suitable header 2B is provided and this is connected to a source ofair under moderate pressure.

The refractory core is made in the manner al` ready described, that isto say, flrst a bottom layer 30 of a dry refractory mix is tamped intoplace, then an iron core 3| is placed in position and refractorygranular material 32 is tamped; around the core 3|. Then the coil 2|) isenergized which induces a current in the core or shell 3| sintering alayer 33 of the refractory material 32, thereby forming a cylindricallining. The iron shell 3| melts in this process. An iron charge can beintroduced into the furnace during the sintering of the lining, in whichcase the iron lcore 3| simply becomes part of the charge.

By forcing air. gas or other suitable coolants between the asbestoscylinders Il and I2, cooling vof the refractory lining is effected and asharper temperature gradient is achieved, keeping the loose grains ofrefractory material in the lining 32 relatively cool and rapidlyfreezing any metal that may leak Ithrough the sintered layer 33. Itshould be understood that thisV type of furnace purposely has acomparatively thin crucible formed of the sintered layer 33 and thebottom sintered layer 40, and a thick crucible wall is not, desired,because whenever a crack starts, it usually runs through the entiresintered wall.

no further than the sintered layer. By keeping the outside of the loosegranular lining 32 relatively cool and making the temperature gradientas steep as possible, the slag from the melt will be more viscous andwill congeal closer to the metal charge than it will if the outsidetemperature ls higher. This early congealing of the 'slag retardschemical reaction with the refractory and thereby promotes longer lininglife.

'Ihe furnace of the invention is a safer furnace because when eventuallythe lining does give out there is a warning as the metal chargepenetrates the asbestos ycylinder l2 because the In these furnades Aacrack can gov metal will run down through the air passage. 'I'hesefurnaces can become dangerous if the metal charge reaches the inductioncoil 20 and penetrates to the circulating water inside of it.

Suitable temperature indicating apparatus. may l be installed in theofftake bustle pipe to indicate increasing destruction of lining or whenlining becomes unsafe through erosion.

It will thus be seen that there has been provided by this invention amethod and an apparatus in which the various objects hereinabove setforth together with many thoroughly v practical advantages aresuccessfully achieved.

As manypossible embodiments may be made of the above invention and asmany changes might be made in the embodiment above set forth, itn

is to be understood that all matter hereinbefore set forth, or shown inthe accompanying drawing, is to be interpreted as illustrative and notin a limiting sense.

I claim: l

An induction\furnace comprising an asbestos box, a refractorybottom insaid asbestos box, a sprally wound hollow induction coil inside of saidbox whereby water may be circulated through the coil, a furnace wallhaving a passage inside of said induction coil, connections sage whichis cooled by the air under pressure and which thereby cools therefractory granular material to cause a steep temperature gradientbetween the crucible and the wall, thereby quickly to freeze any metalor slag penetrating the sintered crucible to increase the life of thelining.

. HENRY'C. FISHER.

